1. Field of the Invention
The invention relates to an electromagnetic transducer, and more particularly to a magnetoresistive element utilizing a magnetoresistive effect usable for magnetic recorders.
2. Description of the Related Art
As a scaling down and an increase in a capacity of magnetic recorders have been required, the requirement for an improvement of a high density magnetic recording technique have been on the increase. The electromagnetic transducer utilizing the magnetoresistive effect (MR effect) is capable of providing regenerative power, for which reason a development of the technique utilizing the magnetoresstive effect is essential and important for improvement of the high density magnetic recording.
Such magnetoresistive transducer or a MR head is disclosed in IEEE Transactions on Magnetics, Vol. MAG-7, No. 1, March 1971 "A Magnetoresistive Readout Transducer". The MR head requires an application of a unidirectional magnetic field onto a magnetoresistive film (Ni--Fe film) for controlling magnetic domains of the film wherein the magnetoresistive film has a magnetic sensitivity to an external magnetic field.
In order to reduce Barkhausen noise, such Ni--Fe magnetoresistive film has a magnetosensitive film whose opposite ends are laminated thereon with antiferromagnetic films such as Fe--Mn films so that a unidirectional magnetic field is generated due to a switched connection at an interface between the Ni--Fe film and the antiferromagnetic film thereby resulting in the unidirectional magnetic field being applied to the magnetic sensitive portion. Such technique is disclosed in the U.S. Pat. No. 4,103,315 issued to Hempstead et al.
According to the technique disclosed in the above U.S. patent, the Ni--Fe magnetoresistive film having the magnetic sensitivity is formed continuously to the antiferromagnetic film for generating a unidirectional magnetic field for control of the magnetic domains. For that reason, when the antiferrormagnetic film is formed to apply the unidirectional magnetic field to the magnetic sensitive portion of the Ni--Fe film, then the continuous formation of the Fe--Mn antiferromagnetic film to the Ni--Fe magnetoresistive film results in a magnetization at opposite ends of the magnetic sensitive portion being fixed due to the switched connection between the Fe--Mn antiferromagnetic film to the Ni--Fe magnetoresistive film. The fixed magnetization may provide a deterioration in sensitivity to the external magnetic field. An outside portion of the Ni--Fe magnetoresistive film positioned outside the magnetic sensitive portion and a soft magnetic film for bias receive influences of a magnetic flux a track other than the readout track thereby resulting in a generation of undesirable noises.
To settle the above problems, the Ni--Fe film is formed only on the magnetic sensitive portion and hard magnetic films are formed at opposite ends of the Ni--Fe film for magnetizations thereof to generate the unidirectional magnetic field to thereby apply the magnetic field onto the magnetic sensitive portion. This technique is disclosed in the Japanese laid-open patent application No. 3-125311.
According to the technique disclosed in the Japanese laid-open patent application No. 3-125311, the magnetoresistive film or the bias soft magnetic film resides only on the magnetic resistive portion thereby the device is free from the problem with the influences by the magnetic flux from the track other than the readout track. This technique, however, provides the following problem. Due to an actual limitation of an accuracy in alignment in process for forming a magnetic head or the MR head, electrode films provided at opposite ends of the magnetoresistive film tend to superimpose the opposite end portions thereof thereby the actual width of the track is narrower than the predetermined width thereof, resulting in a reduction of the output power.
Under the above circumstances, it have been required to develop a novel magnetoresistive element free from the above problems.